Thermo-Responsive Hydrogel for Direct-Write Printing
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Solution Overview
Problem
Current 3D printing inks, such as PLURONIC F127, lack sufficient yield strength and the ability to form covalent crosslinks as both an aqueous liquid and hydrogel, limiting their application in tissue engineering and drug delivery due to their non-covalent interactions and shear-thinning properties.
Innovation Solution
A crosslinkable composition comprising water, a shear-thinning, thermo-responsive polyether triblock copolymer, a water-soluble crosslinking agent with methylenethiol groups, and a photoinitiator capable of abstracting hydrogen from a thiol group under UV light, allowing for photo-crosslinking and forming covalently crosslinked structures suitable for direct-write printing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PLURONIC F127 gel is used as a 3D printing ink, then the composition is easy to extrude and form patterns, but the yield strength is insufficient and covalent crosslinks cannot be formed
Solution Approach 1:
The patent combines PLURONIC F127 triblock copolymer with thiol-containing crosslinking agents and photoinitiators to create a composite hydrogel system. The F127 provides the base gel structure and extrudability, while the thiol-crosslinking network adds covalent bonds for enhanced strength, resolving the contradiction between ease of operation and mechanical strength.
Solution Approach 2:
The patent modifies the chemical parameters of the F127 system by incorporating ene groups into the polymer structure and adding thiol crosslinkers. This transforms the material from a purely physical gel to a chemically crosslinked hydrogel, changing the bonding mechanism from non-covalent to covalent interactions, thereby increasing yield strength while maintaining extrudability.
2Adaptability or versatility
If PLURONIC F127 gel is used, then the material remains liquid at low temperature for printing, but it lacks the ability to form covalent crosslinks as both liquid and hydrogel
Solution Approach 1:
The patent incorporates photoinitiators and thiol crosslinking agents into the F127 composition before printing. This preliminary incorporation allows the material to undergo photo-crosslinking immediately after extrusion or at designated stages, enabling covalent network formation in both liquid and gel states without requiring additional processing steps or equipment modifications.
Solution Approach 2:
The patent introduces thiol-containing crosslinking agents as intermediaries that bridge the F127 polymer chains. These crosslinkers contain both thiol groups for covalent bonding and are compatible with the aqueous F127 system, serving as a mediator that enables crosslinking capability while maintaining the overall material compatibility and simplicity of the printing process.
3Ease of operation
If the composition is made shear-thinning for easy extrusion, then the material flows well during printing, but the yield strength is reduced
Solution Approach 1:
The patent creates a dynamic material system where the F127 hydrogel exhibits shear-thinning behavior during extrusion (reducing viscosity for easy flow) but rapidly recovers its gel structure and yield strength after deposition. The thiol-crosslinking network provides a permanent structural framework that maintains strength even as the material dynamically responds to shear stress during printing.
Solution Approach 2:
The patent utilizes the periodic nature of the printing process (extrusion followed by deposition and setting) to exploit shear-thinning during the extrusion phase, then allows the material to recover its full gel strength during the deposition and crosslinking phases. This periodic action between flowing and gelling states enables both easy extrusion and sufficient yield strength.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The composition provides improved dimensional stability and mechanical properties, enabling the creation of self-supporting structures with enhanced yield stress and resolution, suitable for tissue engineering and biomedical applications.
Implementation Method 1
a photoinitiator capable of abstracting hydrogen from a thiol group when exposed to ultraviolet light of wavelength 10 nm to 400 nm
Implementation Method 2
each of the blocks A comprises a random copolymer of i) a first repeat unit of formula (2)... and ii) a second repeat unit of formula (3)... wherein L′ is a monovalent C1-C10 hydrocarbon radical comprising an ene group (*—CH═CH2) capable of undergoing a thiol-ene reaction
Implementation Method 3
the composition is a liquid at a temperature between 0° C. and about 10° C. and a shear-thinning viscoelastic solid at a temperature of about 15° C. to about 45° C. before crosslinking
Implementation Method 4
the composition is a liquid at a temperature between 0° C. and about 10° C. and a shear-thinning viscoelastic solid at a temperature of about 15° C. to about 45° C. before crosslinking
Data Source
AI summary
A thermo-responsive shear-thinning photo-curable composition comprises water, a linear amphiphilic polyether ABA triblock copolymer comprising at least one pendent ene group (*—CH═CH2) capable of undergoing a thiol-ene reaction, a water-soluble crosslinking agent comprising two or more methylenethiol groups (*—CH2SH), and a photoinitiator. Under non-shear conditions and a triblock copolymer concentration suitable for direct-write printing, the composition is a viscoelastic solid (hydrogel) at a temperature of about 15° C. to about 45° C., and is a free-flowing liquid (sol) between 0° C. and about 10° C. The hydrogel form can be shear-thinned at about 15° C. to about 45° C. to form a sol suitable for a direct-write printer using an extruding print-head. The compositions covalently crosslink when flood-exposed to ultraviolet radiation. The compositions have utility in forming three-dimensional scaffolds for growing living cells.